Integrated circuit packages, such as a quad flat package (QFP), small outline integrated circuit (SOC) package and plastic single small outline (PSSO) package include a die pad and an integrated circuit (or die) that is supported on the surface of the die pad. An encapsulating material surrounds the integrated circuit. A plurality of pins, often called leads, such as “gull wing” leads, usually extend from the sides of the encapsulating material forming the package. The leads are connected by bond wires to the encapsulated integrated circuit. Often these types of integrated circuit devices are formed as surface mounted devices. The package form may be a flat rectangular body and often is a square body with leads extending along all four sides. There are numerous design variations, which differ usually in the number of leads, their pitch, the package dimensions, and the materials used to construct the package. Materials often are selected to improve or vary the thermal characteristics of the package.
The encapsulating material is formed from a molding compound, such as an epoxy or other plastic material, that may sometimes not adhere well to the leads, in which case the molding compound forming the encapsulating material will separate from one or more of the leads. This separation can be induced by temperature changes and is known as delamination. It occurs usually at the point of internal stress at the end of the lead near the die where the bond wire is attached. For many packages the bond wire is formed of gold and the lead tips have been coated with silver to promote the wire bonding. The molding compound used for the encapsulating material usually bonds well with copper but does not bond well with silver and the delamination occurs between the molding compound and any silver coating and causes a wire bond failure from the delamination. Some packages replace the gold wire with a copper wire for cost saving but this creates a greater chance of lead tip delamination and causes a more severe wire bond failure.